There are essentially two different processes for retreading tires. One is the so-called hot cap process, and the other is the so-called pre-cure process. In the pre-cure process, a strip of rubber having a tread formed therein is wrapped about the outer periphery of the tire casing after the old tread has been removed, the casing sprayed with cement, and a layer of uncured rubber interposed between the outer periphery of the casing and the inner periphery of the tread strip. The thus formed assembly is thereafter subjected to heat and pressure to vulcanize the tread onto the casing.
In the course of vulcanizing a pre-cured tread onto a casing, the casing is mounted on a split rim assembly which engages the bead of the tire to support its inner periphery. An inner tube is placed in the casing and inflated to support the casing against the pressure applied. Before mounting the tire and tube on the rim assembly, however, it has been customary to place a flap of rubber between the inner periphery of the tube and the inside of the casing adjacent its bead. The purpose of the rubber flap is to protect the tube from being damaged by the rim.
In each vulcanizing cycle, the support tube is alternately heated and cooled and alternately inflated and deflated. During the heating phase of the cycle, temperatures in a range of 210.degree. F. to 315.degree. F. are applied to the tube for 90-240 minutes while the tube is maintained inflated at a pressure of about 100 psi. The lower temperatures require longer dwell times than higher temperatures. Thereafter, during the cooling phase the tube is deflated and allowed to cool toward room temperature to permit dismounting of the tire casing and remounting of another on the split rim.
While the use of a protective rubber flap between the tube and the rim extends the life of the inner tube somewhat, it has certain limitations. For instance, a substantial amount of labor is required to position the reinforcing layer properly between the tube, the tire casing and the rim if the desired degree of protection is to be achieved. However, even when protective flaps are used in combination with conventional highway-type tubes, the tubes last for only about five to ten cure cycles. When heat resistant-type tubes are used, the tube can last for approximately sixty to seventy cure cycles before failure. Regardless of which type tube is used, approximately 90% of the tube failures occur in the zone where the protective flap is placed.